1. Field of the Invention
This invention relates to an output control circuit that produces a plurality of output control signals derived from one input signal where the leading edges of the control signals occur in a predetermined sequence while the trailing edges occur in a reverse sequence. The invention also relates to an FM stereo receiver which employs an output control circuit of the foregoing type.
2. Discussion of the Prior Art
Conventional output control circuits of the foregoing type use a plurality of Schmidt circuits where the bias of the first stage transistors of each circuit is different. An example of such circuitry is shown in FIG. 1, where 1 is a first Schmidt circuit. Schmidt circuit 1 comprises a first stage transistor 2, an after stage transistor 3, and resistors 4-10. 11 is a second Schmidt circuit. Schmidt circuit 11 similarly comprises a first stage transistor 12, an after stage transistor 13, and resistors 14-20. Resistors 5 and 15 are connected between the respective base and ground of first transistors 2 and 12 where resistor 5&lt;resistor 15. 21 and 22 are power supply terminals of first and the second Schmidt circuits 1 and 11; 23 is a common input signal source connected to the base of first stage transistors 2 and 12; and 24 and 25 are output terminals connected to the collectors of after stage transistors 3 and 13.
As mentioned above, resistors 5 and 15 that are connected between the respective base and ground of first stage transistors 2 and 12 where resistor 5&lt;resistor 15. Consequently, as shown in the FIG. 2(A) input signal waveform, when this input signal falls as shown in the diagram, first stage transistor 2 of first Schmidt circuit 1 first becomes nonconductive. Accordingly, after stage transistor 3 of Schmidt circuit 1 becomes conductive, which causes the output voltage at output terminal 24 of Schmidt circuit 1 to drop as shown in FIG. 2(B). Subsequently, first stage transistor 12 of second Schmidt circuit 11 becomes nonconductive, and accordingly, the output voltage of output terminal 25 of Schmidt circuit 11 similarly drops as shown in FIG. 2(C). On the other hand, when the input signal shown in FIG. 2(A) rises as shown in the diagram, first stage transistor 12 of second Schmidt circuit 11 first becomes conductive. Accordingly, after stage transistor 13 of Schmidt circuit 11 becomes nonconductive, which causes the output voltage at output terminal 25 of Schmidt circuit 11 to rise as shown in FIG. 2(C). Subsequently, first stage transistor 2 of first Schmidt circuit 1 becomes conductive, and accordingly, the output voltage at output terminal 24 of Schmidt circuit 1 similarly rises as shown in FIG. 2(B).
As described above, a conventional output control circuit uses a plurality of Schmidt circuits and, by changing the bias of the respective first stage transistors, it causes a plurality of output voltages originating from one input signal to rise with staggered timing and to fall with staggered timing in the reverse sequence. Consequently, in such an output control circuit, the number of transistors used substantially increases because Schmidt circuits are used. Thus, the circuitry tends to be complicated and costly.